C2.4 Is Bigger Better? Science 10

Why are cells so small?  Cells are small so they can be efficient in transporting materials across their membranes.  If cells were larger then they would need more molecules transported across the cell surface so the cell could function.

 It is not the fact that a larger cell would need more molecules transported in to it that makes it less efficient then a small cell it is the fact that when a cell gets larger the surface area (SA) to volume (v) ratio decreases.  If a cell is bigger it has a greater volume, thus needs for more molecules. To accommodate this it needs a greater surface area to allow these molecules in.  Therefore, molecules that have a higher surface area to volume ratio are more efficient.

What about for Temperature?

Small vs Large  Side= 1.0cm  SA= 6(1.0cm) 2 =6cm 2  V= (1.0cm) 3 = 1cm 3  SA / V = 6cm 2 /1cm 3  SA to V ratio = 6  Side= 2.5cm  SA= 6(2.5cm) 2 =37.5cm 2  V= (2.5cm) 3 = cm 3  SA / V = 37.5cm 2 /15.625cm 3  SA to V ratio = 2.4 Assume the following cells are cubes. The smaller cell has a better SA to V ratio therefore is more efficient then the larger cell.

 In larger cells it is also important to note that it takes longer for nutrients to get to the cells organelles, and also longer for toxins to leave the cell. This greatly affects the cells chances of living Which red dot will leave the cell the fastest?

Maximizing Potential  Multicellular organisms have developed other internal transport systems to reduce dependence on diffusion.  In humans for example, the circulatory system, digestive system and respiratory systems are involved in the transport of essential materials to all the cells of the body.

 In humans, no one cell is more than 0.1mm away from a capillary that transports blood to bring nutrients and remove wastes.  Plants have also developed transport systems outside of cell diffusion.  The xylem is concerned with the delivery of water where the phloem distributes sugars throughout the plant.  These plant transports can carry molecules 100m in some large trees.

 Animals:  Alveoli in the lungs increase surface area for transport o f oxygen and carbon dioxide  Villi from the intestines increase surface area to absorb nutrients Structures in animals and plants that increase surface area  Plants:  Root hairs that extend off plant's roots increase surface area to absorb water and nutrients

Cell # Length (cm) Width (cm) Height (cm) Surface Area (A) Volume (v) S.A to Vol Ratio Start by drawing each cell, then begin to make your calculations.

Activities  Page 293 (Learn and Connect - all)  Study for C2.0 Quiz by doing section review questions on page 294 and 295